1. What is Contact Lens Power Calculation?

The contact lens power calculation converts glasses prescription to contact lens prescription by accounting for the vertex distance between the glasses and the eye. This is necessary because contact lenses sit directly on the eye while glasses sit some distance away.

2. How Does the Calculator Work?

The calculator uses the contact lens power formula:

Where:

• \( CL\ Power \) — Contact lens power in diopters (D)
• \( Glasses\ Power \) — Spectacle lens power in diopters (D)
• \( VD \) — Vertex distance in meters (m)

Explanation: The formula compensates for the change in effective power that occurs when moving the lens from the glasses position to the corneal surface.

3. Importance of Vertex Distance

Details: Vertex distance becomes increasingly important with higher power lenses. The standard vertex distance is typically 12mm (0.012m) for most glasses.

4. Using the Calculator

Tips: Enter your glasses prescription in diopters (include + or - sign) and the vertex distance in meters. For most people, the default vertex distance of 0.012m (12mm) is appropriate.

5. Frequently Asked Questions (FAQ)

Q1: When is vertex distance adjustment necessary?
A: For prescriptions above ±4.00 D, vertex distance becomes clinically significant and should be accounted for.

Q2: What's the typical vertex distance?
A: Standard vertex distance is 12-14mm (0.012-0.014m) for most glasses frames.

Q3: Do I need this calculation for low prescriptions?
A: For prescriptions below ±4.00 D, the difference is usually negligible in practice.

Q4: How does this affect plus vs minus lenses?
A: Plus lenses require stronger contact lens power, while minus lenses require weaker contact lens power compared to glasses.

Q5: Should I use this calculation for multifocal contacts?
A: Multifocal contact lens fitting is more complex and should be done by an eye care professional.